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Correct comment for do_page_fault_process_vm()

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This commit is contained in:
Masamichi Takagi
2017-07-03 10:41:24 +09:00
parent 090937a5a3
commit 72b8f99d3b
1 changed files with 13 additions and 7 deletions
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20
kernel/process.c
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@ -1794,13 +1794,19 @@ static int do_page_fault_process_vm(struct process_vm *vm, void *fault_addr0, ui
}
/*
* XXX: quick fix
* Corrupt data was read by the following sequence.
* 1) a process did mmap(MAP_PRIVATE|MAP_ANONYMOUS)
* 2) the process fetched the contents of a page of (1)'s mapping.
* 3) the process wrote the contents of the page of (1)'s mapping.
* 4) the process changed the contents of the page of (1)'s mapping.
* 5) the process read something in the page of (1)'s mapping.
* Fix for #284
* Symptom: read() writes data onto the zero page by the following sequence.
* (1) A process performs mmap(MAP_PRIVATE|MAP_ANONYMOUS)
* (2) The process loads data from the VM range to cause a PF
* to make the PTE point to the zero page.
* (3) The process performs write() using the VM range as the source
* to cause a PF on the Linux side to make the PTE point to the zero page.
* Note that we can't make the PTE read-only because [mckernel] pseudo
* file covering the range is created with O_RDWR.
* (4) The process stores data to the VM range to cause another PF to perform
* copy-on-write.
* (5) The process performs read() using the VM range as the destination.
* However, no PF and hence copy-on-write occurs because of (3).
*
* In the case of the above sequence,
* copy-on-write pages was mapped at (2). And their physical pages